Probably silly how I'm going for O2 after yesterday's events of their services being down but my wife has a phone on an O2 contract which has been fully paid off and is ready for an upgrade, she doesn't care about new phones and is going to give me the upgrade and keep her old phone with the upgrade sim. Can I use my own non-O2 sim (EE) in the new O2 phone?
Read more: https://iphoneus.org/faq/will-an-iphone-x-on-a-o2-contract-be-unlocked.html